High-current pulsed ion source



June 16, 1964 MCFARLAND 3,137,820

HIGHCURRENT PULSED ION SOURCE Filed May 1, 1958 United States Patent3,137,820 HIGH-CURRENT PULSED ION SQURCE George C. McFarland, Berkeley,Caiif., assignor to High Voltage Engineering Corporation, Burlington,Mass, a corporation of Massachusetts Filed May 1, 1958, Ser. No. 732,3604 Claims. (Cl. 328-458) somewhat diagrammatic view showing the ionsource of v the invention in longitudinal central section and includinga diagram of the associated circuit.

Referring to the drawing, ions are produced within a chamber 1 thelateral wall 2 whereof preferably is made of glass or other insulator. Agrounded flange 3 is supported at one end of the lateral wall 2 and ananode 4 is supported at the opposite end thereof. A suitable gas to beionized is admitted into the chamber 1 in accordance with techniqueswell known in the art. High-voltage pulses are produced by means to bedescribed in detail hereinafter and are applied between the groundedflange 3 and the anode 4 so that the anode 4 is periodically raised tohigh positive voltage. As a result of this, a high voltage discharge isinitiated periodically within the chamber 1, and the positive ions inthis discharge are extracted by an extractor 5 to which negative voltageis applied by means to be described in detail hereinafter.

In order to produce the various voltages hereinbefore referred to, ahigh-voltage pulse-forming network 6, including several condensers 7connected in parallel, is: charged by a high-voltage power supply 8 towhich it is connected through a current limiting resistor 19. Thepulse-forming network 6 may, for example, have its components sodesigned as to provide a substantially squarewave pulse of 10microseconds duration. The condensers 7 of the pulse-forming network 6are discharged through a suitable switch mechanism, such as a 5022hydrogen thyratron 9 whose plate 10 is connected to the high-voltage endof the pulse-forming network 6 and whose cathode 11 is connected to theanode 4 of the ion-source chamber 1. The thyratron cathode 11 is alsoconnected to ground through a blocking resistor 12. The hydrogenthyratron 9 is fired at suitable intervals by any conventional pulsingmechanism 13 connected to the grid 14 of the thyratron.

Just before the thyratron is fired, the anode 4 of the ion-sourcechamber 1 is at ground potential since it is connected to ground throughthe blocking resistor 12. When the thyratron 9 is fired, the anode 4 ofthe ionsource chamber 1 is immediately raised to high positive voltage,since it is now connected through the thyratron 9 to the high voltageend of the pulse-forming network 6. An intense electric field is thusgenerated within the chamber 1 between the anode 4 and the groundedflange 3, so that a discharge is initiated within the chamber 1. Withthis discharge there is associated a large flow of cur rent within thechamber 1 between the anode 4 and the grounded flange 3, and thiscurrent is supplied from the charge stored in the condensers 7 of thepulse-forming network 6. When the condensers 7 of the pulse-formingnetwork 6 have been discharged, the gas-discharges cease in the chamber1 and in the thyratron 9, so that the thyratron 9 is againnon-conducting and the anode 4 is at ground potential. The condensers 7of the pulse-forming network 6 are then recharged by the high-voltagepower supply 8, and the cycle is repeated.

3,137,820 Patented June 16, 1964 During the discharge within the chamber1 a negative pulse is applied to the ion extractor 5, thereby creatingan electric field which extends from the ion extractor 5 to within theaperture 15 in the grounded flange 3, so as to pull positive ions out ofthe chamber 1. In order to produce the required negative voltage at theextractor 5, the low voltage end of the pulse-forming network 6 isconnected to ground through the primary 16 of a pulse transformer 17.The secondary 18 of the pulse transformer 17 is connected to the ionextractor 5, so that during the discharge of the pulse-forming network 6a voltage pulse of about 50 to 250 kilovolts negative is applied to theion extractor 5. Because of the high currents involved during the pulse,very high ion beam currents are possible.

While the invention has been described with particular reference to theproduction of positive ions, the invention is not limited thereto, butis equally applicable to the production of negtaive ions by means ofappropriate reversals of potentials in the apparatus hereinbeforedescribed.

Summarizing then, in order to provide high currents of ions, positiveand negative, the invention uses an ion discharge tube conducting to1000 amperes with high voltage extraction as described hereinbefore.

Having thus described the principles of the invention together with anillustrative embodiment thereof, it is to be understood that althoughspecific terms are employed they are used in a generic and descriptivesense and not for purposes of limitation, the scope of the inventionbeing set forth in the following claims.

I claim:

1. An ion source for the production of high currents of ions, consistingof an ion discharge tube having an apertured electrode and an anode,means for introducing a suitable gas to be ionized into said iondischarge tube, means for applying high-voltage pulses between saidapertured electrode and said anode so that said anode is periodicallyraised to a positive voltage sufficiently high to initiate an ionizationdischarge within said ion discharge tube, a pulse-forming networkadapted to deliver high current to said anode during said pulses tosupport said ionization discharge, an extractor electrode adapted toextract ions of one polarity from said ion discharge tube uponapplication of high voltage of opposite polarity to said extractorelectrode and means for applying high-voltage pulses of said oppositepolarity to said extractor electrod during delivery of said high-currentpulses to said ion discharge tube.

2. An ion source for the production of ion currents of the order ofamperes, consisting of an ion discharge tube having an aperturedelectrode and an anode, means for introducing a suitable gas to beionized into said ion discharge tube, means for applying high-voltagepulses between said apertured electrode and said anode so that saidanode is periodically raised to a positive voltage sufficiently high toinitiate an ionization discharge within.

said ion discharge tube, a pulse-forming network for delivering currentof the order of 10 to 10 amperes to said anode during said pulses tosupport said ionization discharge, an extractor electrode adapted toextract ions of one polarity from said ion discharge tube uponapplication of high voltage of opposite polarity to said extractorelectrode and means for applying voltage of the order of 10 volts ofsaid opposite polarity to said extractor electrode during delivery ofsaid high-current pulses to said ion discharge tube.

3. An ion source for the production of high currents of ions, consistingessentially of an ion discharge tube having an apertured electrode andan anode, means for introducing a suitable gas to be ionized into saidion discharge tube, a high-voltage pulse-forming network, having ahigh-voltage power supply and a switching device associated therewith,for applying high-voltage pulses between said apertured electrode andsaid anode so that said anode is periodically raised to a positivevoltage sufiiciently high to initiate an ionization discharge withinsaid ion discharge tube, and including an LC circuit adapted to deliverhigh current to support said ionization discharge, an extractorelectrode adapted to extract ions of one polarity from said iondischarge tube upon application of high voltage of opposite polarity tosaid extractor electrode and means, energized by the flow of currentupon discharge of said pulse-forming network by said switchingmechanism, for applying high voltage of said opposite polarity to saidextractor electrode.

4. An ion source for the production of high currents of ions, comprisingan ion discharge tube having a grounded apertured electrode and ananode, the aperture in said grounded electrode being adapted to effectthe egress of ions generated in said ion discharge tube, means forintroducing a suitable gas to be ionized into said ion discharge tube, ahigh-voltage pulse-forming network, having a highvoltage power supplyand a switching device associated therewith, for applying high-voltagepulses between said apertured electrode and said anode so that saidanode is periodically raised to a positive voltage sufficiently high toinitiate an ionization discharge within said ion discharge tube,including an LC circuit adapted to deliver high current to support saidionization discharge, an extractor electrode disposed externally of saidtube and proximate to said apertured electrode such that the electricfield thereof extends through said aperture to extract ions of onepolarity from said ion discharge tube upon application of high voltageof opposite polarity to said extractor electrode, and a pulsetransformer of which the primary is so connected that the dischargecurrent from said pulse-forming network flows therethrough, whereby ahigh-voltage pulse is produced by the secondary of said pulsetransformer, and means for applying said high-voltage pulse to saidextractor electrode.

References Cited in the file of this patent UNITED STATES PATENTS2,214,608 Bull Sept. 10, 1940 2,444,921 Dawson et al. July 13, 19482,820,142 Kelliher Jan. 14, 1958 2,856,532 Martina Oct. 14, 1958 OTHERREFERENCES Electronics Applied to the Betatron (Dietze and Dickinson).Reprinted from the Proceedings of the I.R.E., vol. 37, No. 10, October1949, pages 1171-1178.

1. AN ION SOURCE FOR THE PRODUCTION OF HIGH CURRENTS OF IONS, CONSISTINGOF AN ION DISCHARGE TUBE HAVING AN APERTURED ELECTRODE AND AN ANODE,MEANS FOR INTRODUCING A SUITABLE GAS TO BE IONIZED INTO SAID IONDISCHARGE TUBE, MEANS FOR APPLYING HIGH-VOLTAGE PULSES BETWEEN SAIDAPERTURED ELECTRODE AND SAID ANODE SO THAT SAID ANODE IS PERIODICALLYRAISED TO A POSITIVE VOLTAGE SUFFICIENTLY HIGH TO INITIATE AN IONIZATIONDISCHARGE WITHIN SAID ION DISCHARGE TUBE, A PULSE-FORMING NETWORKADAPTED TO DELIVER HIGH